The needs and desires of stellar population models Scott Trager
The needs and desires of stellar population model users Scott Trager
Desires/motivation We want to know the star formation histories of galaxies to determine when and how they form How do we do this? Mean ages and distribution of stellar ages Abundances track nucleosynthetic processes which track star-formation time scales via sites of element production
What do we want? Models that cover extended wavelength region to study the variety of stellar populations in galaxies (FUV to NIR) at galaxy-like resolution with excellent empirical calibration different populations contribute in different wavelength regions: FUV: EHB stars, OB stars NUV: BHB stars, hot MSTO stars Optical: cool MSTO stars, RGB NIR: AGB stars
What do we want? Models that take into account abundance ratio variations consistently over entire wavelength region with same resolution as full models
What do we need? Depends on what we want: Abundances for nucleosynthesis analysis: Models with self-consistent, fully computed interior and atmospheres for [X i /Fe] 0 empirically calibrated on real stellar populations Star formation histories for individual galaxies Wide wavelength region to determine ages and compositions of different sub-populations
What are we looking forward to? 30m telescopes and JWST: higher and higher redshifts younger and younger stellar populations the near- and thermal-ir in nearby galaxies RGB/AGB/RSG/LPVs... do we understand them all? (Italy v Ukraine and Germany v Argentina!)
What can we do now? Determine the star-formation histories of small, nearby galaxies from colour-magnitude diagrams e.g. Gallart et al. (2005) but useful/crucial to have abundance information (Tolstoy et al. 2003)
What can we do now? Model UV/optical/NIR SEDs (magnitudes, colours, and surface-brightness fluctuations) and their evolution Tinsley (1968); Bruzual (1983); Charlot & Bruzual (1991); Bruzual & Charlot (1993, 2003), GRASIL (Silva et al. 1998)
What can we do now? Break age-metallicity degeneracy for single-age, single-metallicity (SSP) populations Worthey (1994), Buzzoni (1994), and many following
What can we do now? Model galaxy spectra in detail Gunn, Stryker & Tinsley (1981); Bruzual (1983); Bell & Houdashelt (1996): purely theoretical spectra+models; Vazdekis (1999)
What can we do now? Account for [α/fe] 0 Pioneered by Bell & Houdashelt (1996), followed by Greggio (1997); Tantalo et al. (1997); Trager et al. (2000); Thomas et al. (2003) May even be able to model [N/Fe], [C/Fe], [Ca/Fe] others?
What can we do now? Match photometric and spectroscopic ages for real SSP s 47 Tuc: Gibson et al. (1999) found that Worthey (1994) models give t>20 Gyr from absorption lines while isochrones give t~14±1 Gyr
What can we do now? Finally solved by Schiavon et al. (2002a,b)? [α/fe] 0, RGB/AGB LF wrong in models, problems with atmospheric parameters of stellar library, CN bimodality... Schiavon (this workshop) claims to fit M67, 47 Tuc, NGC 6528 with proper ages and compositions; Lee & Worthey (2005) claim to fit many globulars with [α/fe] 0
What can t we do now? We cannot (yet?) decompose multiple populations using absorption-line strengths alone Recent attempts (e.g. Schiavon et al. 2006) are promising but may be model-dependent Spectral fitting is promising (see, e.g., Panter, this workshop) but has long history (stretching back to Whipple 1935!) Empirical calibration?
What can t we do now? Model absorption-line strengths with selfconsistent interior+atmosphere models when [X i /Fe] 0 or even when [α/fe] 0 Model detailed galaxy spectra when [α/fe] 0 promising work by Coelho et al. (this meeting) especia!y in blue and NUV can only now predict colours when [α/fe] 0! and how do we calibrate them?
What s coming? Models with self-consistently modeled interiors +atmospheres when [X i /Fe] 0 Not perfect, but on more solid ground than current models At least two groups are reaching for this: Worthey, Chaboyer, Baron, Trager, Lee, Dotter... Charlot, Weiss, Bruzual, Coelho, Salaris...
What can you do? If you take data, take stellar libraries of different kinds of stars for example: Bulge giants and dwarfs Dwarf galaxy giants and dwarfs in different bands: NUV, optical, NIR galaxies at all redshifts and many wavelengths
What can you do? If you make interior models, use realistic and consistent boundary conditions many normal and weird elemental mixtures and if you make isochrones, use a variety of mass-loss parameters/rules
What can you do? If you make model atmospheres and synthetic spectra, use realistic and consistent opacities many normal and weird elemental mixtures
What can you do? If you make synthesis models, use these new interior and atmosphere models make your models as modular as possible so that different ingredients can be used and tested against observations
What can you do? For every model maker and ingredient provider --- interiors, atmospheres, synthesis models, stellar libraries --- use standardised exchange formats to ensure modularisation of stellar population models, ease of use, and ease of comparison
Conclusions We ve came a long way since Whipple (1935)......and there s a lot of work still do!
Thanks for coming, from your hosts!
Thanks for coming, from your hosts!
Thanks for coming, from your hosts! Perhaps First light on stellar populations in 2008?